As a lubricant for plastically working metallic material usually used a graphite which is dispersed in oil or in water. The former is a lubricant in which graphite is dispersed in a composition obtained by adding an extreme pressure additive and wax in mineral oil, but there is a risk of smoke or ignition due to oil when used in warm or hot temperature which causes great problems in safety, working environment and health. The latter is a lubricant in which an extreme pressure additive is added to water and graphite is dispersed therein, there is no risk of smoking or ignition compared to oil base lubricant, and also exhibits excellent lubrication performance. However, as long as graphite is used, the workers and working environment are contaminated black and there are problems in health.
In order to solve the problem of these working environments, attempts have been made to develop a lubricant for plastic working which does not use graphite. For example, it is known a water-soluble lubricant for hot plastic working consisting essentially of (a) resin powder such as cellulose resin, acrylic resin or the like having a specific particle size distribution, (b) alkali metal salt of isophthalic acid and adipic acid, (c) water-soluble high polymer such as carboxymethyl cellulose, and (d) the balance being water (Patent Literature 1).
However, in Patent Literature 1, there is no example in which a polyester resin is used as the resin (a), and even in the specification, a polyester resin is usable but there is no description as to whether it is hydrophilic or hydrophobic. In addition, the metal materials processed in the examples are all iron materials such as S45C and S35C.
Further, as lubricants for cold plastic working, Patent Literatures 2 to 4 and the like are known. In these cold plastic working lubricants, under severe environments such as spray coating on high temperature molds and subsequent warm and hot plastic working of aluminum materials, there is a problem that the adhesion amount to the mold decreases and the strength of the lubricating coating film is insufficient, due to insufficient heat resistance of the lubricant.